1. Field of the Invention
The present invention relates to apparatus and methods of producing hydrocarbon. Particularly, the present invention relates to apparatus and methods of stimulating the production of hydrocarbon by removing liquid from the wellbore. More particularly, the present invention relates to apparatus and methods of removing liquid from the wellbore by installing a pumping unit downhole in a well having a safety valve.
2. Description of the Related Art
In the oil and gas production industry, and more specifically in the production of natural gas, water encroachment into the wellbore presents significant difficulties in maintaining production output. Generally, water in the produced fluid is not problematic if water only makes up small portion of the produced fluid. In small quantities, the water will typically remain in droplet form, and the velocity of the produced gas flowing from the formation into the wellbore and up to surface will often be sufficient to entrain the water droplets and carry the droplets to surface.
However, as the proportion of water in the produced fluid increases, the hydrostatic pressure increases because the density of the gas/water droplet column in the wellbore rises. The increase in hydrostatic pressure decreases the pressure gradient between the gas-producing formation and the section of wellbore which intersects the formation. As a result, hydrocarbon flowing into the wellbore from the formation is limited.
Furthermore, the level of water in the produced fluid adversely affects the velocity of the gas moving to the surface. The velocity of the gas may be reduced to a level insufficient to carry the water droplets out of the well, thereby increasing the rate of hydrostatic pressure buildup. In some cases, the increase in hydrostatic pressure may kill the well.
All of these problems are particularly acute in depleted wells; that is, wells that have been producing for some time and that the formation pressure has diminished to a level of economic or physical unfeasibility.
One temporary solution used in the industry is installing velocity strings in the wellbore. Velocity strings are designed to restrict the cross-sectional flow area up the wellbore, thereby increasing the velocity of the produced gas as it travels up the wellbore. However, velocity strings create significant flow restrictions in the wellbore, which leads to lower production rates. In addition, the restricted strings may also cause the velocity of the gas to drop below the rate necessary to carry the water droplets to surface. Eventually, the well is again killed.
Artificial lift systems are commonly employed to assist in the recovery of hydrocarbons. A simple form of an artificial lift system may include a pumping unit disposed downhole. The deployment of the pumping unit, such as an electrical submersible pump, usually requires a cable extending back to the surface. Once downhole, the pumping unit may be operated to pump the water to surface, thereby reviving the well.
However, the deployment of the pumping unit in an offshore well presents various challenges. Offshore wells are often equipped with a surface controlled subsurface safety valve (“scssv”). In many instances, the safety valve is a legal requirement. Safety valves are generally used as a safety device to ensure that if the fluid conduit between the ocean floor and the platform is disrupted, the flow of production fluid from the sub-sea well head will be cut off and the ocean will not be contaminated with production fluid. One obstacle to installing a pumping unit downhole is the inability to run the cable or other connection means through the safety valve while keeping the safety valve operational. Particularly, the safety valve can not close and seal properly with the cable extending therethrough.
To overcome this problem, it is known to remove the entire production string and replace it with a modified production string. In this arrangement, the cable is disposed in the annulus defined by the modified string and the casing. However, this solution typically involves expensive workover equipment which may be uneconomical for a marginal well.
There is a need, therefore, for an apparatus and method of operating a pumping unit disposed below a safety valve. There is also a need for an apparatus and method for installing a downhole cable and a safety valve assembly. Further, there is a need for an apparatus and method to install an artificial lift system to revive a well.